mbta_vehicles

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The readOnlyHint annotation already signals a safe read operation. The description adds value by naming the returned fields (GPS coordinates, speed, bearing, current status) and noting it covers active vehicles. It does not disclose additional limitations like data freshness or pagination, but these are not critical for this simple tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two focused sentences, front-loaded with the main action, no fluff. Every word earns its place, making it easy to parse quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple tool with only two optional parameters and no output schema, the description covers the essentials: what it returns, which transit system, and the filtering option. It could mention alternatives or response format, but the description is adequate for its simplicity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema already provides full descriptions for both parameters (limit and route), including examples and a default. The description's 'Optionally filter by route' adds no new information beyond the schema, so it does little to enhance parameter understanding.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool gets live vehicle positions for MBTA (Boston), with specific data fields (GPS coordinates, speed, bearing, current status). This distinguishes it from sibling tools like mbta_routes, mbta_alerts, and mbta_predictions, as well as other agencies' vehicle tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description indicates the tool is for live vehicle positions and mentions optional filtering by route, providing clear user context. However, it does not explicitly mention when not to use it or alternatives such as mbta_predictions for arrival times, so it stops short of full exclusion guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.